Again, the evil Team Rocket is causing chaos across the region, and it is up to the player to defeat them.

Changes from Red and Green

Kanto is aesthetically redesigned, with the design of doors, signposts and other tilesets redesigned. Cerulean Cave, the game's final dungeon, receives the most significant overhaul, sporting a completely different layout. These designs would later be reused for the international Pokémon Red and Blue. Indigo Plateau remains unaltered.

All Pokémon have new front sprites but retain the same back sprites from Red and Green. Trainers and the literal Ghost have the same sprites from Red and Green. The sprites from Blue would later be used in the international Pokémon Red and Blue.

The introduction of the game features a battle between a Gengar and a Jigglypuff, as opposed to a Gengar and a Nidorino, as it was in Pokémon Red and Green. This change carried on into the localized version of Pokémon Blue, while the original appeared in the localized Pokémon Red.

The places where some Pokémon are obtainable was changed:

Jynx and Lickitung, only available through in-game trades in Red and Green, are now found in the wild.

A glitch that allows the player to surf from the top of a cliff was removed.

A glitch where the game mistakenly believes the player has beaten Sabrina (when they actually lost to her) was removed.

MissingNo. was given the placeholder Pokédex entry コメント さくせいちゅう Comment to be written. and became the ??? species. This was not translated, resulting in a glitched Pokédex entry in the localized Pokémon Red and Blue and the corruption of MissingNo.'s original height and weight (1.0 m (3.3 ft) and 10.0 kg (22.1 lb), respectively), showing instead a height of 10.0 ft (3.1 m) and a weight of 3507.2 lb (1590.8 kg).[3]

The following Pokémon could be found in Red and Green Versions but are not obtainable in Pokémon Blue. In order to obtain any of the below Pokémon, they must be traded from one of the paired versions of Generation I, or from Generation II. The table below indicates which paired Generation I game has that Pokémon available.

Note that G marks the Pokémon obtainable in Pokémon Green, which has the same available Pokémon as Western Blue.

Trades between Pokémon games in different languages are possible; however, a Japanese game cannot connect with a non-Japanese game without causing corruption. This is due to the fact that the games cannot automatically translate the Pokémon data from Japanese to a different language or vice versa, since neither game fully encodes both kana and the Latin alphabet (only encoding one fully and the other partially). If a battle between a Japanese game and a non-Japanese game is attempted, the battle simply does not work, with the save files left unharmed.

Virtual Console

The Nintendo 3DSVirtual Console release uses 3DS wireless communication as a substitute for the Game Link Cable. Japanese and non-Japanese Generation I core series games do not recognize each other when attempting to link them via 3DS wireless communication.

Using Poké Transporter, the entirety of Box 1 can be sent from the Generation I core series games to Pokémon Bank (regardless of language), from where they can be withdrawn in the Generation VII core series games.

Differences in the Virtual Console release

The Nintendo 3DS Virtual Console release can link with other Virtual Console Generation I and II core series games via Nintendo 3DS wireless communication, simulating the Game Link Cable. When initiating a link, the Virtual Console menu on the touch screen replaces the Cable Club attendant's dialogue.

Trivia

The man who trades the player an Electrode on Cinnabar Island claims that the Raichu he received "went and evolved". As Raichu does not have an evolved form, this is not possible. However, in the context of Japanese Pokémon Blue, it makes sense as the player trades away a Kadabra, which evolves through trade, for a Graveler.

The old man who trades the player a Jynx in Cerulean City claims that the Poliwhirl he received "went and evolved". As Poliwhirl cannot evolve via trade in Generation I, this is not possible. However, in the context of Japanese Pokémon Blue, the old man trades away a Haunter for a Machoke, which does evolve through trade.